1. Field of the Invention
The present invention relates to a nanoemulsion based on a surfactant which is solid at a temperature of less than or equal to 45xc2x0 C., which surfactant is chosen from glycerol fatty esters, and on at least one oil having a molecular weight of greater than 400, the ratio by weight of the amount of oily phase to the amount of surfactant ranging from 2 to 10.
The invention also relates to a process for the preparation of the nanoemulsion and to its uses in the cosmetics, dermatological and/or ophthalmological fields. This nanoemulsion is stable on storage and can contain large amounts of oil while retaining good transparency and while having good cosmetic properties.
2. Discussion of the Background
Nanoemulsions are oil-in-water emulsions, the oil globules of which have a very fine particle size, i.e. a number-average size of less than 100 nm. They are generally manufactured by mechanical fragmentation of an oily phase in an aqueous phase in the presence of a surfactant. In the case of nanoemulsions, the very small size of the oily globules is obtained in particular by virtue of at least one pass through a high-pressure homogenizer. The small size of the globules confers on them cosmetically advantageous properties which distinguish them from conventional emulsions: they are transparent and exhibit a novel texture. They can also carry active principles more efficiently.
Transparent microemulsions are known in the art. In contrast to nanoemulsions, microemulsions are not, strictly speaking, emulsions. Rather, microemulsions are transparent solutions of micelles swollen by oil, which oil is generally a very-short-chain oil (e.g. hexane or decane) and is solubilized by virtue of the joint presence of a significant amount of surfactants and of cosurfactants which form the micelles. The size of the swollen micelles is very small owing to the small amount of oil which they can solubilize. This very small size of the micelles is the cause of their transparency, as with nanoemulsions. However, in contrast to nanoemulsions, microemulsions are spontaneously formed by mixing the constituents, without contributing mechanical energy other than simple magnetic stirring. The major disadvantages of microemulsions are related to their necessarily high proportion of surfactants, leading to intolerance and resulting in a sticky feel during application to the skin. Furthermore, their formulation range is generally very narrow and their temperature stability very limited.
In addition, nanoemulsions are known in the art that contain an amphiphilic lipid phase composed of phospholipids, water and oil. These emulsions exhibit the disadvantage of being unstable on storage at conventional storage temperatures, namely between 0 and 45xc2x0 C. They lead to yellow compositions and produce rancid smells which develop after several days of storage.
Nanoemulsions stabilized by a lamellar liquid crystal coating, obtained by the combination of a hydrophilic surfactant and of a lipophilic surfactant, are also known. However, these combinations are difficult to prepare. Furthermore, the nanoemulsions obtained exhibit a waxy and film-forming feel which is not very pleasant for the user.
EP-A-728,460 discloses nanoemulsions based on fluid non-ionic amphiphilic lipids. However, these nanoemulsions disadvantageously exhibit a sticky effect during application to the skin.
The need therefore remains for nanoemulsions which have neither the disadvantages of those of the prior art nor the disadvantages of microemulsions.
It has now been found that, surprisingly, the use of a surfactant which is solid at a temperature of less than or equal to 45xc2x0 C., which surfactant is chosen from glycerol fatty esters, and of at least one oil having a molecular weight of greater than 400 (=400 grams per mole) makes it possible to obtain novel nanoemulsions exhibiting all the advantages of known nanoemulsions, such as described above, without their disadvantages.
Accordingly, the first embodiment of the present invention relates to a nanoemulsion, that includes:
an oily phase dispersed in an aqueous phase; and
at least one glycerol fatty ester surfactant which is solid at a temperature of less than or equal to 45xc2x0 C.;
wherein the oily phase includes oil globules having a number-average size of less than 100 nm;
wherein the oily phase includes at least one oil having a molecular weight of greater than 400; and
wherein a weight ratio of the oily phase to the surfactant ranges from 2 to 10.
Another embodiment of the present invention relates to a composition selected from the group including a topical composition, an ophthalmic vehicle, a pharmaceutical composition, a dermatological composition, a cosmetic, and an opthalmological composition, and mixtures thereof, that includes the above-noted nanoemulsion.
Another embodiment of the present invention relates to a method for caring for, treating and/or making up the skin, face and/or scalp, that includes applying to the skin, face and/or scalp the above-noted nanoemulsion.
Another embodiment of the present invention relates to a method of caring for and/or treating the hair, that includes applying to the hair the above-noted nanoemulsion.
Another embodiment of the present invention relates to a method of caring for and/or moisturizing the skin, mucous membranes and/or scalp, that includes applying to the skin, mucous membranes and/or scalp the above-noted nanoemulsion.
Another embodiment of the present invention relates to a process for preparing the above-noted nanoemulsion, that includes:
mixing an aqueous phase and an oily phase with stirring at a temperature ranging from 10 to 80xc2x0 C. to form a mixture; and
homogenizing the mixture at a pressure ranging from 6xc3x97107 Pa to 18xc3x97107 Pa.
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description of the preferred embodiments of the invention.
The nanoemulsions according to the invention preferably have a transparent to bluish appearance. Their transparency is measured by a transmittance coefficient at 600 nm ranging preferably from 10 to 90% or else by a turbidity ranging from 60 to 600 NTU and more preferably from 70 to 300 NTU, which turbidity is measured with a Hach Model 2100 P portable turbidimeter. These ranges include all values and subranges therebetween.
The oil globules of the nanoemulsions of the invention have a number-average size of less than 100 nm and preferably ranging from 20 to 75 nm and more preferably from 40 to 60 nm. These ranges include all values and subranges therebetween. The decrease in the size of the globules makes it possible to promote the penetration of the active principles into the surface layers of the skin (carrier effect).
The surfactant is a glycerol fatty acid ester which is solid at all temperatures less than and equal to 45xc2x0 C. Most preferably, the nanoemulsion of the invention contains only a surfactant chosen from glycerol fatty esters and it is devoid of any surfactant other than glycerol fatty esters.
The glycerol fatty esters which can be used as surfactants in the nanoemulsions according to the invention are solid at a temperature of less than or equal to 45xc2x0 C. and are preferably chosen from the group including of esters formed from at least one acid having a saturated linear alkyl chain, having from 16 to 22 carbon atoms, and from 1 to 10 glycerol units. One or more of these glycerol fatty esters can be used in the nanoemulsion of the invention.
These esters are preferably chosen in particular from stearates, behenates, arachidates, palmitates and their mixtures. Stearates and palmitates are most preferably used.
Preferred examples of surfactant which can be used in the nanoemulsion of the invention include decaglycerol monostearate, distearate, tristearate and pentastearate (CTFA names: Polyglyceryl-10 stearate, Polyglyceryl-10 distearate, Polyglyceryl-10 tristearate, Polyglyceryl-10 pentastearate), such as the products sold under the respective names Nikkol Decaglyn 1-S, 2-S, 3-S and 5-S by the company Nikko, and diglycerol monostearate (CTFA name: Polyglyceryl-2 stearate), such as the product sold by the company Nikko under the name Nikkol DGMS.
Preferably, the amount of surfactant in the nanoemulsion of the invention can range, for example, from 0.2 to 15% by weight and more preferably from 1 to 8% by weight with respect to the total weight of the nanoemulsion. These ranges include all values and subranges therebetween.
The ratio by weight of the amount of the oily phase to the amount of surfactant ranges from 2 to 10 and preferably from 3 to 6. These ranges include all values and subranges therebetween. The term amount of oily phase is understood here to mean the total amount of the constituents of this phase without including the amount of surfactant.
The nanoemulsion according to the invention contains at least one oil with a molecular weight of greater than 400. The oils with a molecular weight of greater than 400 can be preferably chosen from oils of animal or vegetable origin, mineral oils, synthetic oils and silicone oils, and their mixtures. Mention may be made, as oils of this type, of, for example, isocetyl palmitate, isocetyl stearate, avocado oil or jojoba oil.
In addition, the oily phase can optionally contain other oils and in particular oils having a molecular weight of less than 400. These oils are also preferably chosen from oils of animal or vegetable origin, mineral oils, synthetic oils and silicone oils. Mention may be made, for example, as more preferred oils with a molecular weight of less than 400, of isododecane, isohexadecane, volatile silicone oils, isopropyl myristate, isopropyl palmitate or C11-C13 isoparaffin.
The oily phase can also contain fatty substances other than the oils indicated above, such as fatty alcohols, for example stearyl, cetyl and behenyl alcohols, fatty acids, for example stearic, palmitic and behenic acids, oils of fluorinated type, waxes, gums and their mixtures.
The nanoemulsions in accordance with the invention contain an amount of oily phase preferably ranging from 2 to 40% and more preferably from 5 to 30% by weight with respect to the total weight of the nanoemulsion, the proportion of oil(s) having a molecular weight of greater than 400 preferably representing at least 40% by weight of the oily phase. These ranges include all values and subranges therebetween.
According to a preferred embodiment of the invention, the nanoemulsion of the invention additionally contains one or more ionic amphiphilic lipids.
Preferred ionic amphiphilic lipids which can be used in the nanoemulsions of the invention may be chosen from the group formed by anionic amphiphilic lipids, cationic amphiphilic lipids and alkylsulphonic derivatives.
Preferably, the anionic amphiphilic lipids can be chosen from the group formed by:
the alkaline salts of dicetyl and dimyristyl phosphate;
the alkaline salts of cholesterol sulphate;
the alkaline salts of cholesterol phosphate;
lipoamino acids and their salts, such as mono- and disodium acylglutamates, such as the disodium salt of N-stearoyl-L-glutamic acid sold under the name Acylglutamate HS21 by the company Ajinomoto;
the sodium salts of phosphatidic acid;
phospholipids.
The alkylsulphonic derivatives can be preferably chosen from the alkylsulphonic derivatives of following formula (I): 
in which R represents an alkyl radical having from 16 to 22 carbon atoms, more preferably the C16H33 and C18H37 radicals, taken as a mixture or separately, and M is an alkali metal, such as sodium.
The cationic amphiphilic lipids can be preferably chosen from the group formed by quaternary ammonium salts, fatty amines and their salts.
Preferred quaternary ammonium salts include, for example:
those which exhibit the following general formula (II): 
xe2x80x83in which the R1 to R4 radicals, which can be identical or different, represent a linear or branched aliphatic radical having from 1 to 30 carbon atoms or an aromatic radical, such as aryl or alkylaryl. The aliphatic radicals can include heteroatoms, such as, in particular, oxygen, nitrogen, sulphur or halogens. The aliphatic radicals are preferably chosen from alkyl, alkoxy, polyoxy(C2-C6)alkylene, alkylamido, (C12-C22)alkylamido(C2-C6)alkyl, (C12-C22)alkyl acetate or hydroxyalkyl radicals having approximately from 1 to 30 carbon atoms; X is an anion preferably chosen from the group including the halides, phosphates, acetates, lactates, (C2-C6)alkyl sulphates, or alkyl- or alkylarylsulphonates. Preference is given, as quaternary ammonium salts of formula (II), to, on the one hand, tetraalkylammonium chlorides, such as, for example, dialkyldimethylamrnmonium or alkyltrimethylammonium chlorides in which the alkyl radical has about 12 to 22 carbon atoms, in particular behenyltrimethylammonium, distearyldimethylammonium, cetyltrimethylammonium and benzyldimethylstearylammonium chlorides, or alternatively, on the other hand, stearamidopropyldimethyl(myristyl acetate)ammonium chloride, sold under the name Ceraphyl 70 by the company Van Dyk;
imidazolinium quaternary ammonium salts, such as, for example, those of following formula (III): 
xe2x80x83in which R5 represents an alkenyl or alkyl radical having from 8 to 30 carbon atoms, for example derived from tallow fatty acids; R6 represents a hydrogen atom, an alkyl radical having from 1 to 4 carbon atoms or an alkenyl or alkyl radical having from 8 to 30 carbon atoms; R7 represents an alkyl radical having from 1 to 4 carbon atoms; R8 represents a hydrogen atom or an alkyl radical having from 1 to 4 carbon atoms; and X is an anion preferably chosen from the group of the halides, phosphates, acetates, lactates, alkyl sulphates, or alkyl- or alkylarylsulphonates. R5 and R6 preferably denote a mixture of alkenyl or alkyl radicals having from 12 to 21 carbon atoms, for example derived from tallow fatty acids, R7 preferably denotes a methyl radical and R8 preferably denotes hydrogen. Such a product is, for example, sold under the name Rewoquat W 75 by the company Rewo;
quaternary diammonium salts of following formula (IV): 
xe2x80x83in which R9 denotes an aliphatic radical having approximately from 16 to 30 carbon atoms;
R10, R11, R12, R13 and R14 are chosen from hydrogen or an alkyl radical having from 1 to 4 carbon atoms; and X is an anion preferably chosen from the group of the halides, acetates, phosphates, nitrates and methyl sulphates.
Preferred quaternary diammonium salts include in particular propanetallowdiammonium dichloride.
According to a preferred embodiment of the invention, a lipoamino acid is used as the ionic amphiphilic lipid.
Preferably, the ionic amphiphilic lipids can be introduced into one or other phase of the nanoemulsion. When they are present in the nanoemulsion of the invention, they can be used in concentrations preferably ranging from 0.01 to 5% by weight and more particularly from 0.25 to 1% by weight with respect to the total weight of the nanoemulsion. These ranges include all values and subranges therebetween.
The emulsions in accordance with the present invention can optionally contain additives for improving the transparency of the formulation.
These additives are preferably chosen from the group formed by:
lower alcohols having from 1 to 8 carbon atoms and more particularly from 2 to 6 carbon atoms, such as ethanol;
glycols, such as glycerol, propylene glycol, 1,3-butylene glycol, dipropylene glycol, pentylene glycol, isoprene glycol and polyethylene glycols having from 4 to 16 and preferably from 8 to 12 ethylene oxide units;
sugars, such as glucose, fructose, maltose, lactose or sucrose.
These additives can be used as a mixture. When they are present in the nanoemulsion of the invention, they can be used at concentrations preferably ranging from 0.01 to 30% by weight, more preferably from 0.3 to 25% by weight, and most preferably from 5 to 20% by weight with respect to the total weight of the nanoemulsion. The amount of alcohol(s) and/or of sugar(s) preferably ranges from 5 to 20% by weight and more preferably from 10 to 15% by weight with respect to the total weight of the nanoemulsion and the amount of glycol(s) preferably ranges from 5 to 15% by weight with respect to the total weight of the nanoemulsion. These ranges include all values and subranges therebetween.
To obtain preservative-free emulsions, it is preferred to use the alcohols as defined above at concentrations greater than or equal to 15% by weight with respect to the total weight of the nanoemulsion.
The nanoemulsions defined above can be used in any field where this type of composition is useful. They are particularly useful in compositions for topical use and, most particularly, cosmetic or dermatological compositions. They can also be used as ophthalmic vehicles. In addition, they are especially useful in the pharmaceutical field, a pharmaceutical composition which can be administered orally, parenterally or transcutaneously.
Another preferred embodiment of the invention is therefore a composition for topical use, characterized in that it contains a nanoemulsion as defined above.
Preferably, a composition for topical or pharmaceutical use contains a physiologically acceptable medium, i.e. compatible with the skin, mucous membranes, scalp, eyes and/or hair.
Another preferred embodiment of the invention is an ophthalmic vehicle, characterized in that it contains a nanoemulsion as defined above.
Another preferred embodiment of the invention is a pharmaceutical composition, characterized in that it contains a nanoemulsion as defined above.
Preferably, the nanoemulsions of the invention can optionally contain water-soluble or fat-soluble active principles having a cosmetic, dermatological or ophthalmic activity. The fat-soluble active principles are in the oily globules of the emulsion, whereas the water-soluble active principles are in the aqueous phase of the emulsion. Preferred examples of active principles include vitamins, such as vitamin E, and their derivatives and in particular their esters, provitamins, such as panthenol, humectants and sun-screen agents.
Preferred ophthalmic active principles include, for example, antiglaucoma agents, such as betaxolol; antibiotics, such as acyclovir; antiallergics; anti-inflammatory agents, such as ibuprofen and its salts, diclofenac and its salts, or indomethacin; or antiviral agents.
The nanoemulsions in accordance with the invention can be provided in the form of a lotion, serum, cream, milk or toilet water and can contain adjuvants commonly used in the cosmetics, dermatological and ophthalmic fields, such as, for example, gelling agents, preservatives, antioxidants and fragrances. They can also be provided in the form of an eye lotion, in particular for ophthalmological applications.
Preferred gelling agents which can be used include cellulose derivatives, algal derivatives, natural gums and synthetic polymers, such as polymers and copolymers of carboxyvinyl acids, for example those sold under the name Carbopol by the company Goodrich.
Another preferred embodiment of the invention is a process for the preparation of a nanoemulsion as defined above, this process including the mixing of the aqueous phase and the oily phase with vigorous stirring at a temperature ranging from 10 to 80xc2x0 C. and then a homogenization of the mixture at a pressure preferably ranging from 6xc3x97107 Pa to 18xc3x97107 Pa (high-pressure homogenization). The shearing (e.g. mixing or stirring) preferably ranges from 2xc3x97106 sxe2x88x921 to 5xc3x97108 sxe2x88x921 and better still from 1xc3x97108 sxe2x88x921 to 3xc3x9710 sxe2x88x921 (sxe2x88x921 signifies second xe2x88x921) The nanoemulsion of the invention can be most preferably used, for example, for caring for, treating or making up the skin, face and/or scalp.
Another preferred embodiment of the invention is therefore the cosmetic use of the nanoemulsion as defined above for caring for, treating and/or making up the skin, face and/or scalp.
Preferably, the nanoemulsion of the invention can also be used for caring for and/or treating the hair. It makes it possible to obtain a deposit of oil on the hair, which renders the latter glossier and more resistant to styling, without, however, making it lank. It also makes it possible, as a pretreatment, to improve the effects of dyeing or permanent waving.
Another preferred embodiment of the invention is therefore the cosmetic use of the nanoemulsion as defined above for caring for and/or treating the hair.
The nanoemulsion according to the invention is excellent for moisturizing the skin, mucous membranes and/or scalp and is particularly suited to the treatment of dry skin.
Another preferred embodiment of the invention is therefore a cosmetic process for caring for and/or moisturizing the skin, mucous membranes and/or scalp, characterized in that a nanoemulsion as defined above is applied to the skin, mucous membranes and/or scalp.
Another preferred embodiment relates to the use of the nanoemulsion according to the invention in the manufacture of a dermatological composition intended for the treatment of dry skin.
Another preferred embodiment relates to the use of the nanoemulsion according to the invention in the manufacture of an ophthalmological composition.